Protecting software against illegal copying by users is very difficult, and such protection is of genuine economic interest.
Proposals have been made to protect certain high-value software packages against illegal copying by associating the software with an external memory, e.g. of the ROM type, which memory must be plugged into an input/output port of the microcomputer on which the software is run. If the external memory is not connected to the microcomputer, then it is not possible to use the corresponding software. Such a portection system suffers from being passive. A fraudulent user merely has to analyze the signals interchanged between the external memory and the microcomputer in order to be subsequently capable of simulating an external memory, thereby defeating the protection.
In order to avoid this drawback, proposals have also been made to associate a main data medium on which the software to be protected is recorded with a removable data medium which is loaded into a device which is auxiliary to the main apparatus on which the software is run. A portion of the software is stored on the removable medium. The main portion of the software stored on the main hard disk of the microcomputer is insufficient for enabling the software as a whole to run. The removable medium is preferably of the electronic memory type card with access to the card memory being controlled. This solution improves software protection against copying, but it suffers from the drawback of requiring numerous interchanges between the main apparatus on which the software is being run and the auxiliary device in which the memory card is inserted, thereby significantly reducing the speed of executing of the software.
An object of the invention is to provide a method of running software which is protected against illegal copying, the method providing the same degree of protection as the system described above, but reducing transit times between the main apparatus on which the software is run and the auxiliary device.